Bulletin Board

Aug 2010: EPA announces its selection of the vapor intrusion remedy for the MEW Superfund Study Area in EPA’s Record of Decision Amendment for the Vapor Intrusion Pathway (Click Here). EPA thanks the community for comments received on the Proposed Plan & for participating in the decision making process.

Description and History

NPL Listing History

NPL Status: Final

Proposed Date: 10/15/84

Final Date: 02/11/91

Deleted Date:

The 56-acre former Fairchild Semiconductor Corp. - Mountain View facilities manufactured semiconductors and is located in Mountain View, California. The Fairchild Semiconductor Corp - Mountain View site is one of three Superfund or National Priorities List (NPL) sites that are being cleaned up simultaneously. The other two Superfund sites are the Intel - Mountain View site and the Raytheon site. All three sites are located in the Middlefield-Ellis-Whisman (MEW) Study Area and are being addressed collectively as the MEW SIte. Site investigations at several of these facilities during 1981 and 1982 revealed extensive soil and groundwater contamination, primarily volatile organic compounds (VOCs).

Fourteen potential sources of contamination have been identified at the former Fairchild facilities, including underground and aboveground storage tanks for chemical products and wastes, pH neutralization systems, and industrial wastewater treatment systems.

Who is Involved

Investigation and Cleanup Activities

The contamination addressed in the MEW Record of Decision is both facility-specific and regional. Each individual MEW Company is responsible for investigation, cleanup, and source control for soil and groundwater contamination at their individual facility-specific properties south of U.S. Highway 101. Contaminated groundwater that has bypassed the source control areas and has mixed together with other contaminated groundwater from other source areas is considered part of the regional groundwater contamination plume, or the “regional plume.”

The MEW Regional Groundwater Remediation Program systems south and north of U.S. Highway 101 are designed to contain and clean up contaminated groundwater where it has mixed together with other contaminated groundwater and where the source of contamination has not been identified. The Navy and NASA both operate groundwater extraction and treatment systems to contain and clean up contaminated groundwater at their areas of responsibility on Moffett Field, in addition to the regional system operating North of 101 on Moffett Field.

It is important to note that groundwater currently is not used for drinking water or other potable uses. Groundwater in the area is, however, a potential future source of drinking water and therefore groundwater cleanup standards have been established.

Remedy Selected

In June 1989, EPA issued a Record of Decision selecting the soil and groundwater cleanup remedy for the MEW Site. The soil remedy includes: excavation, with treatment by aeration; and soil vapor extraction with treatment by vapor-phase granular activated carbon. The groundwater remedy includes: slurry walls (barriers beneath the surface) to contain contaminants; and extraction and treatment systems to contain and clean up groundwater contamination using granular activated carbon and/or air-stripping systems.
Because the groundwater contamination at the MEW Site migrates northward and has mixed with contamination from sources at the NAS Moffett Field Superfund site, the groundwater remedy selected in the MEW Record of Decision also applies to the commingled regional groundwater contamination area on former NAS Moffett Field (the West-Side Aquifers), but not the entire former NAS Moffett Field facility.

515/545 Whisman Road and 313 Fairchild Drive (Former Buildings 1-4)

In 1986, Fairdhild installed a 40-foot deep slurry wall was installed in 1986 along the boundaries of these properties to limit migration of chemicals, and was keyed into the A/B aquitard. Groundwater extraction was initiated in the mid-1980s to control and clean up sources in the groundwater. The system was expanded and currently includes 12 source control extraction wells both inside and outside the slurry wall. The MEW Regional Program operates three wells outside the slurry wall. Treatment systems 1 and 3 have treated over an estimated 900 million gallons of groundwater and removed over 34,000 pounds of VOCs from the groundwater through December 2006.

401 National Avenue (Former Building 9)

In 1986, Fairchild installed a slurry wall along the boundaries of this property and that was keyed into the A/B aquitard at a depth of approximately 40 feet. Groundwater extraction began at this property in 1982 from well 65A. Since then, the groundwater system has been expanded to include four source control extraction wells within the slurry wall enclosure. Extracted groundwater from the five A Aquifer wells is treated at System 1. Three other source control extraction wells (GSF-1A, GSF-1B1, and GSF-1B2) have also been installed north of this facility and are the joint responsibility of Vishay/SUMCO and Fairchild/Schlumberger.

369 and 441 North Whisman Road (Former Buildings 13, 19, 23)

In 1986, Fairchild installed an approximately 40-foot-deep slurry wall along the boundaries of the 369 North Whisman Road property, keyed into the A/B aquitard. Groundwater extraction began in 1982 at this property, and was expanded to include seven A Aquifer source control extraction wells within the slurry wall enclosure; two A Aquifer source control extraction wells downgradient of the slurry wall to the north; three source control extraction wells in the B1 Aquifer; and two source control extraction wells in the B2 Aquifer. Groundwater extracted from these wells is piped to System 19, located at 369 North Whisman Road, for treatment. System 19 has treated over 800,000 gallons of groundwater and removed over 10,000 pounds of VOCs from the groundwater through December 2006.

644 National Avenue (Former Building 18)

One source control extraction well (RW-25A) currently operates in the A Aquifer northwest of the building. Groundwater from this extraction well is treated at System 1. System 1 also treats water from two basement-dewatering sumps at 644 National Avenue.

464 Ellis Street (Former Building 20)

No potential sources were found at this property. Raytheon installed and currently operates two source control extraction wells in the A and B1 Aquifers, respectively. These wells capture contaminants immediately downgradient of the Raytheon slurry wall. Groundwater from the two wells is conveyed to the Raytheon system at 350 Ellis Street for treatment.

EPA First Five-Year Review

EPA's 2004 Five-Year Review for the MEW Study Area determined that for the groundwater remedy to remain protective in the long-term, the following actions need to be taken: long-term protectiveness should continue to be verified by monitoring the extent of groundwater contamination along the estimated groundwater contamination plume boundaries. This evaluation should be accomplished through routine annual groundwater sampling events. Current data indicate that the remedy is functioning as required to meet the remedial action objectives; however, EPA recommends optimization of both the regional and facility-specific systems to enhance plume capture, evaluation of applicable technologies to potentially expedite contaminant mass removal and cleanup time, and evaluation of the potential need for institutional controls.

Current Actions

The MEW Companies, Navy and NASA arepreparing work plans to evaluate other alternate groundwater cleanup technologies to address the MEW Site-wide groundwater contamination.

Site Studies

EPA Evaluates Vapor Intrusion Pathway
The existing soil and groundwater remedy at the MEW Site does not address risks from long-term exposure through the vapor intrusion pathway. Since the issuance of EPA’s 1989 Record of Decision, new information has been developed regarding the toxicity of TCE and potential vapor intrusion into buildings overlying shallow groundwater contamination. In 2003, as part of EPA’s Five-Year Review of the MEW Study Area, EPA began evaluating whether VOCs in shallow groundwater are potentially migrating upward through the soils and cracks in the floors or through plumbing conduits and other preferential pathways, and impacting indoor air.

Based on indoor air sampling of both commercial and residential buildings in the area conducted in 2003 to 2007, EPA has confirmed the presence of the subsurface vapor intrusion pathway into a number of structures overlying the shallow groundwater TCE plume. None of the samples taken to date indicate any immediate or short-term health threat to building occupants from this pathway. EPA’s main concern is whether the chemicals from the Site measured in indoor air pose an unacceptable risk of chronic health effects due to long-term exposure (25 years or more). It is EPA’s policy not to set cleanup levels or take action to reduce levels that are less than ambient background levels.

Some of the sampled buildings indicated indoor air contaminant concentrations that were elevated above background levels and above EPA Region 9’s TCE interim action level in indoor air for long-term exposure. In each of these buildings, the MEW Companies and NASA have taken voluntary interim measures (e.g., sealing cracks/conduits, upgrading/modifying ventilation systems, installing air purifying systems) to reduce the indoor air contaminant concentrations. In addition, many new buildings in the MEW Study Area have taken measures to help prevent or mitigate the vapor intrusion pathway. Although EPA has not yet determined what the long-term mitigation and monitoring strategy should be for all buildings overlying shallow groundwater contamination, the results of these interim measures have generally reduced the indoor air levels thus far and are protective of residents and workers.

In 2010, after amending the MEW Record of Decision, EPA selected a remedy that addressed potential long-term exposure of TCE, and other VOCs at unacceptable levels, through the vapor intrusion pathway, For more information, please access the 2010 Record of Decision Amendment for the Vapor Intrusion Pathway document either by clicking here or finding it in the Records of Decision subsection of the Documents and Reports section below.

In 1985, EPA issued an Administrative Order on Consent to the parties potentially responsible for site contamination. As a result of this Order, the potentially responsible parties conducted an investigation to determine the nature and extent of the site contamination. In 1990, EPA issued an Administrative Order requiring the clean up of the sites and responsibility for the long-term operation of the regional groundwater extraction system.

Cleanup Results to Date

Under EPA’s direction and oversight, the MEW Companies, including Fairchild Semiconductor Corp. and Schlumberger Technology Corp., implemented the soil and groundwater cleanup programs that have included soil excavation and treatment, installation of four slurry walls, soil vapor extraction and treatment systems, and groundwater extraction and treatment systems. The soil cleanup by soil vapor extraction and excavation and aeration has been completed at all the former MEW facilities, including the former Fairchild facilities.

Groundwater cleanup will continue to operate for many decades in order to meet the TCE groundwater cleanup standard of 5 parts per billion. The MEW Site groundwater remedy has removed over 76,000 pounds of contaminants, and has reduced contaminant concentrations throughout the multiple aquifer zones. The groundwater is not being used as a potable water supply, and there are no direct exposure pathways to the contaminated groundwater while groundwater cleanup continues.

Potentially Responsible Parties

Potentially responsible parties (PRPs) refers to companies that are potentially responsible for generating, transporting, or disposing of the hazardous waste found at the site.

Under EPA's direction and regulatory oversight, Schlumberger Technology Corporation is responsible for investigating and cleaning up the soil and groundwater at the Fairchild-Mountain View Superfund Site. In addition, the following individual companies are responsible for investigating and cleaning up the groundwater at the MEW Site. These companies are collectively referred to as the MEW Companies:

Documents and Reports

Community Involvement

Public Meetings: A community advisory group, the MEW Community Advisory Board, meets to learn about and discuss MEW Superfund Study Area investigation and cleanup issues.

EPA has awarded a Technical Assistance Grant (TAG) to the Pacific Studies Center. The TAG provides money for activities that help the community understand technical information at the MEW Site. Please contact Lenny Siegel, TAG Administrator, at 650-961-8918 or LSiegel@cpeo.org for more information.